New test can detect most colon cancer

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NEW YORK — A new noninvasive screening test can detect most cases of colorectal cancer and also many precancerous polyps, potentially helping to sharply reduce the death toll from the disease, according to results of a study released on Thursday.

Still, the results fell short of investor expectations and even those of the company that developed the test, Exact Sciences Corp., sending its shares down about 20 percent in afternoon trading on Thursday.

In its news release about the study Thursday, Exact Sciences said its test detected 92 percent of the cancers picked up by colonoscopy, and 42 percent of potentially precancerous polyps. It had a false positive rate of 13 percent.

The test looks for alterations in human DNA found in a stool sample. The company contends that people will not find it off-putting to deposit a sample of their stool in the company’s collection apparatus and mail it to a laboratory.

The new test, called Cologuard, would not replace colonoscopy. Colonoscopy remains the gold standard for colorectal screening, in part because any polyps detected can also be removed during a colonoscopy, possibly preventing cancer.

But about half of people older than 50, the recommended age to start screening for colorectal cancer, are either not adequately screened or not screened at all, in part because colonoscopy is invasive and time-consuming.